Drop in cannabis disorder numbers

More than 185,000 Australians will no longer be diagnosed with cannabis use disorders under changes to the controversial diagnostic manual used by psychiatrists released this month.

Researchers looked at the revised diagnostic criteria in the latest version of the manual, known as DSM-5, to see if it would have an impact on prevalence. Under DSM-5, cannabis abuse and dependence symptoms were combined into one disorder and included new criteria for withdrawal and craving. When these factors were considered, University of NSW researchers found thousands now categorised as having a cannabis disorder fell below the diagnostic threshold.

An author of the study, Associate Professor Tim Slade, said he was surprised by the finding because a similar study had found a dramatic increase in alcohol use disorders under DSM-5.

''Essentially, the same criteria are being used for both cannabis and alcohol,'' Professor Slade, from the university's National Drug and Alcohol Research Centre, said. ''It's concerning … when you apply the same criteria to one drug and diagnosis goes up, but for another, it goes down.''

Professor Slade put the discrepancy down to abuse criteria being merged with dependence in the new manual. Because cannabis has a higher ratio of abuse to dependence compared with alcohol, more cannabis than alcohol users were likely to drop below the diagnostic threshold. Of those reclassified as no longer having a problem, many were young men, which Associate Professor Slade said might be cause for concern.

''We know from other studies that young men who abuse substances are less likely to seek help … With this transition to them not being considered as having a problem, it may make it even less likely they will seek help.''

But the director of the National Cannabis Prevention and Information Centre at the University of NSW, Jan Copeland, said she was not concerned by the reduction.

''It is not surprising that those who may have been overdiagnosed in the [previous] system that included the concept of abuse are young males more likely to be risk takers and use in hazardous situations - but are not on a predictable pathway to addiction at this stage,'' Professor Copeland said.

''It is not appropriate they are included in a clinical classification system.''